Background

Most of the Indian river ecosystems have been profoundly altered by various human interventions over the last few decades. Human activities such as alteration of flow regimes by construction of dams, sand mining, water pollution, etc., (CPCB, 1996; Nilsson et al., 2005; Padmalal et al., 2008; Swarnkar et al., 2021) cause serious impacts on the river ecosystem. Water pollution, which is a consequent event of anthropogenic activity, emerges as a serious problem that causes alteration of abiotic factors eventually threatening biotic communities within the river ecosystem (Amoatey & Baawain, 2019; Ishaq & Khan, 2013). This water pollution has an adverse impact on aquatic insects community, especially medically important mosquitoes which eventually effects on the epidemiology of mosquito-borne diseases (Buxton et al., 2020; Fazeli-Dinan et al., 2022; Huzortey et al., 2022; Villena et al., 2017).

Mosquitoes act as a primary vector for various diseases such as malaria, dengue, chikungunya, filariasis and Japanese encephalitis etc. (WHO, 2014). Nearly 700 million people are affected by the mosquito borne disease and more than one million deaths in every year worldwide (Chilakam et al., 2023). Bionomics of mosquitoes plays a crucial role to take suitable control measures to curtail mosquito population and disease outbreak (Wu et al., 2020). Mosquito population highly regulates by various abiotic factors, especially water pollution (Huzortey et al., 2022). Water pollution acts main driver to alter the mosquito vector composition in a habitat/area, hinder prey and predator relationship and altering breeding habitats (Huzortey et al., 2022). For instance, polluted water bodies are rendering ideal breeding habitats for Culicine than Anopheline vectors (Gunathilaka et al., 2013; Kamaladhasan et al., 2016). The polluted habitat, particularly high turbid water affects the predatory efficiency due to low visibility of prey (Homski et al., 1994; Paaijmans et al., 2008). Last few decades, several studies reported that Anopheline vectors have adapted to breed in polluted water bodies across the world. For instance, An. gambiae (Awolola et al., 2007; Ossè et al., 2019), An. culicifacies (Gunathilaka et al., 2013, 2015), An. coluzzii (Kudom, 2015; Ossè et al., 2019), An. subpictus (Gunathilaka et al., 2015; Kamaladhasan et al., 2016), An. stephensi (Fazeli-Dinan et al., 2022) were breeding in polluted water bodies. In our previous studies, we reported that human activities within the river bed rendering conducive environment for mosquito breeding through various ecological link for the maintenance of self-sustained mosquito populations along the river ecosystem (Kamaladhasan et al., 2016). These anthropogenic activities are highly modified the river ecosystem especially water quality along the river basin. Therefore, deciphering the how water quality influence on the mosquito ecology at modified river ecosystem is very essential to understand the epidemiology of mosquito-borne diseases and curtail mosquito population. Hence, the present study is aimed to study the community assemblage and habitat similarity of immature mosquito population with reference to water quality at different habitats along the Vaigai River basin.

Methods

Study sites

The Vaigai river bisects the Madurai city into two halves and flows downstream for 145 km and passes 127 km upstream originating from the Cumbum Valley of the Western Ghats. In order to understand the influence of water quality on habitat specificity and community assemblage of immature mosquito populations, three different study sites viz. urban (Madurai city: 9° 55′ N, 78° 07′ E), semi-urban (Sholavandan: 10° 01′ N, 77° 57′ E) and rural (Thenoor; 9º 59′ N; 78º 00′ E) were selected and observations were made on a 5 km linear stretches along the Vaigai river in each study site.

Immature mosquito sample collection

The immature mosquito populations were studied at three different ecosystems viz., urban, semi-urban and rural study sites along the Vaigai river basin. Observations were made during the pre-monsoon, monsoon and post-monsoon seasons of 2013–2014. The larval density of Anopheles, Culex and Aedes were calculated by using dipper method in all the study sites. Based on the immature mosquito populations in habitat, the number of dips per habitat was determined. The number of dips varied from 3 to 10 per habitat depending on the immature mosquito population. The sampling was done on alternate days in all the study sites during the entire period of the study. The immature mosquitoes were collected and transferred to the laboratory, and the emerged adults were collected and identified with the help from Center for Research in Medical Entomology (CRME), Madurai. The species composition and relative frequency of mosquitoes were calculated and the average larval density was measured at all the study sites. The presence and absence of predators in each study site was noted for each sample.

Physico-chemical analysis of water

The physico-chemical parameters such as pH, total dissolved solids (TDS), salinity, conductivity, turbidity, dissolved oxygen (DO) were analyzed using water analysis kit (Systronics, 371). The free carbon dioxide (free CO2) and total alkalinity (TA) were analyzed by standard titration method. Temperature and water depth were measured in habitats with standard instruments.

Data analysis

Grouping of immature mosquitoes based on their habitat similarities

The collected immature mosquitoes were grouped based on their breeding habitat similarity. Data was analyzed according to the method proposed by Devi and Jauhari (2007) and Stein et al. (2011). The operational taxonomic units (OTUs) were given based on the vegetative and non-vegetative habitat types. The vegetation types include the presence of floating algae, filamentous algae, host plant (Cynodon dactylon, Saccharum spontaneum, Cyperus rotundus, Typha sp., Polygonum glabrum, Ipomoea aquatica, Arundo donax, Eichhornia crassipes, Azolla sp., Marsilea sp. and Lemna sp.), algal bloom and the absence of vegetation. The non-vegetative habitat types include rock pools, animal hoofs, waste dumping (cups, polythene bags, etc.), detritus (stumps, leaves, etc.) and cement tanks. The type of habitat sharing among immature mosquitoes was considered as an OTU. The presence or absence of predators inhabiting with immature mosquitoes was also considered as another OTU. Individual OTUs were assigned for each of water quality parameters (pH, TDS, salinity, turbidity, conductivity, DO, free CO2, TA, water depth and temperature) of breeding habitats for each species. All the larval habitat characteristics were subdivided into groups and codified as 1/0 (= presence/absence). A matrix of data consisting of 21 rows for mosquito species and 135 columns for breeding habitats was developed in tabular form based on the codified data. This matrix data was used to analyze the similarity among all OTUs using the Jaccard’s coefficient of association (JC). From the similarity matrix, OTUs were grouped and depicted in the form of a dendrogram.

Results

Relative frequencies of immature mosquitoes at different ecosystem during seasons

The relative frequency of mosquitoes showed greater variations among the study sites and seasons throughout the entire study period. Cx. vishnui was found to be a pervasive species which showed a higher relative frequency (38.46%) than other mosquitoes at urban sites during the pre-monsoon season. In contrast to urban sites, An. subpictus had a high relative frequency in semi-urban and rural study sites during the pre-monsoon season (35.82% and 27.06% respectively). During monsoon season, Cx. vishnui had the highest relative frequency (28.10%) in the urban sites, while An. culicifacies were found to have a higher relative frequency in semi-urban (18.82%) and rural study sites (27.27%). During post-monsoon season, An. subpictus was observed as a more common species and had higher relative frequencies than other mosquito species in all study sites. (Table 1).

Table 1 Mosquito relative frequency (%) at different ecosystems along the Vaigai river, Tamil Nadu
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Average larval density at different study sites during seasons

In urban study site, pre-monsoon and post-monsoon seasons significantly influenced the Anopheles larval density than monsoon season (F = 6.38; p < 0.05). In the case of Culex larval density, monsoon season seemed to have high influence than the other two seasons (F = 8.059; p < 0.05). Oddly, Aedes larval density was not found to be influenced by any seasons (F = 1.123; p > 0.05). In semi-urban study site, Anopheles larval density was strongly influenced by pre-monsoon season than other two seasons (F = 34.25; p < 0.05). Culex larval density was not influenced by any seasons (F = 3.318; p > 0.05). In rural study site, pre-monsoon and post-monsoon seasons significantly influenced the Anopheles larval density than monsoon season (F = 4.457; p < 0.05). Culex larval density was influenced by both pre-monsoon and monsoon seasons than post-monsoon season (F = 3.587; p < 0.05). Aedes larval density was not influenced by any seasons (F = 0.380; p > 0.05) (Fig. 1).

Fig. 1
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Average larval density of Anopheline and Culicine species along the Vaigai river, Tamil Nadu

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Average larval density and presence or absence of predators

In urban site, Anopheles and Culex larval density was found to be higher in habitats without predators when compared to the habitats with predators during the pre-monsoon and monsoon seasons. Higher Anopheles larval density was recorded in habitats without predators when compared to habitats with predators whereas Culex larval density was observed to be maximum in habitats with predators rather than without predators during post-monsoon season. In semi-urban site, higher Anopheles larval density was recorded in habitats without predators when compared to habitats with predators during pre-monsoon and monsoon seasons whereas Anopheles larval density was higher in habitats with predators during post-monsoon season. Culex larval density found to be high in the presence of predators during the pre-monsoon and monsoon seasons. In rural site, Anopheles larval density was greater in habitats without predators than with predators during monsoon and post-monsoon seasons. Culex larval density was found to be high in habitats without predators during all seasons (Fig. 2).

Fig. 2
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Average larval density of Anopheline and Culicine species in habitats with and without predators. AWP, Anopheles larval density with predators; CWP, Culex larval density with predators; AEWP, Aedes larval density with predators; AWOP, Anopheles larval density without predators; CWOP, Culex larval density without predators; AEWOP, Aedes larval density without predators

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Inhabitation of predators along with immature mosquitoes under different vegetation

A total of seven aquatic predators were found to co-exist with immature mosquito populations in all the study sites during the study period. The aquatic predators such as backswimmer, dragonfly, damselfly and diving beetles were observed in all sites. Water bugs were mainly noticed in urban sites whereas fishes and tadpoles were recorded in semi-urban and rural sites. Among the predators, backswimmers were observed in various aquatic vegetation types such as filamentous algae, floating algae, Cyperus rotundus, Polygonum glabrum, E. crassipes, Ipomoea aquatica, Cynodon dactylon, Azolla sp., detritus, algal bloom and in area devoid of vegetation. Dragonfly and damselfly were mainly noticed in sites dominated by filamentous algae. Water bugs were mainly noticed to exist in roots of E. crassipes. Backswimmer inhabited with more number of immature mosquitoes (18/ 21) followed by dragonfly (13/ 21) and water bugs (10/ 21) (Table 2).

Table 2 Inhabitant of predators along with immature mosquitoes in the Vaigai river, Tamil Nadu
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Relative frequency of predators at different ecosystems

During pre-monsoon season, backswimmer showed greater relative frequency at urban (53.33%) and rural sites (61.11%) whereas dragonfly had high relative frequency in semi-urban site (42.11%). Dragonfly had high relative frequency at semi-urban (35.29%) and rural sites (48.15%) during monsoon season. In urban site, backswimmer had maximum relative frequency during monsoon season (40.74%). Dragonfly was found to have high relative frequency in semi-urban site (50%) whereas backswimmer was higher at urban site (38.46%) during post-monsoon season. Backswimmer and dragonfly showed almost equal relative frequency during post-monsoon season in rural site (Table 3).

Table 3 Relative frequency of predators at different study sites along the Vaigai river, Tamil Nadu
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Percentage co-occurrence of predators along with immature mosquito populations

Predators were found to co-exist with immature mosquito populations in all the study sites during the entire study period. At urban study site, the percentage of predator co-occurrence along with larvae was found to be higher during post-monsoon followed by pre-monsoon and monsoon seasons. The percentage co-occurrence of predators was gradually increasing from pre-monsoon to post-monsoon season at rural study site. During the pre-monsoon and monsoon seasons, the percentage of predator co-occurrence was higher in rural whereas the maximum percentage of predator co-occurrence was noted in urban followed by rural and semi-urban site during post-monsoon season (Fig. 3).

Fig. 3
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Percentage co-occurrence of predators along with immature mosquito population along the Vaigai river, Tamil Nadu

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Community assemblage of immature mosquitoes at different study sites

Community assemblage of immature mosquito populations was found to be strongly influenced by seasons in all the sites. During pre-monsoon season, community assemblage of Anopheles with Culex (45.71%) was found to be higher followed by Anopheles community and Aedes community at rural site. In semi-urban site, habitat occupied by Anopheles with Culex was higher followed by Anopheles community during pre-monsoon season. Community assemblage by Culex species alone was not observed in semi-urban and rural sites during pre-monsoon season. In urban site, assemblage of Anopheles with Culex (64%) was maximum followed by Culex alone (30%); Anopheles alone (4%); Aedes with Anopheles and Culex community (2%) during pre-monsoon season. Anopheles with Culex assemblage was observed to be higher in all the study sites during monsoon season. Community assemblage by Anopheles species alone was found to be greater in semi-urban and rural site when compared to Culex community alone during monsoon season. Community assemblage by Anopheles species alone was not observed in urban site during monsoon season. During post-monsoon season, Anopheles community was greater at rural (45.45%) site followed by Anopheles with Culex (40.91%). Anopheles sharing their habitats with Culex (44.44%) mosquitoes were found to be higher at semi-urban whilst community assemblage by Anopheles alone and Culex alone was almost in equal proportion at semi-urban sites during post-monsoon season. In urban site, community assemblage of Anopheles with Culex was observed to be greater followed by Anopheles community and Culex community during post-monsoon season (Table 4).

Table 4 Community assemblage of immature mosquitoes at different study sites along the Vaigai river, Tamil Nadu
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Physico-chemical analysis of water at different study sites

Water quality parameters varied among the sites during all seasons. During the pre-monsoon season, pH, conductivity, dissolved oxygen, total alkalinity and salinity varied in all the study sites. Total dissolved solids, turbidity, free carbon dioxide was higher in the urban site than others. During the monsoon season, pH was found to be higher in rural site when compared to other sites. Salinity, conductivity, turbidity was higher at urban site than other sites whereas total alkalinity, free carbon dioxide and TDS varied in all the sites. During post-monsoon season, pH was found to be higher in rural site than semi-urban and urban sites. Salinity and conductivity didn’t vary among the study sites whereas total alkalinity was higher in semi-urban site than other sites. TDS and turbidity were found to be greater in urban site than semi-urban and rural sites. Free carbon dioxide was found to be lower in rural site when compared to urban and semi-urban sites (Table 5).

Table 5 Physico-chemical characteristics of water at different study sites along the Vaigai river, Tamil Nadu
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Water quality versus mosquitoes

Anopheles diversity was found to be higher in semi-urban followed by rural and urban sites. When comparing with Culex mosquitoes, Anopheles mosquitoes seemed to prefer less polluted water bodies. An. subpictus was found to breed in polluted water bodies with a wide range of TDS (range = 0.53–1010), salinity (range = 0.05–4.39), turbidity (range = 0.38–316) and total alkalinity (range = 0.25–450). An. vagus and An. peditaeniatus were also able to breed in high turbid water (range = 0.93–124 & 1.1–85) than other Anopheles species. Among the Anopheles species, An. annularis and An. stephensi was found to breed in less turbid habitats at low temperature (Table 6). Fredwardsius vittatus was found to breed under high pH with low free carbon dioxide when compared to other mosquitoes. Cx. bitaeniorhynchus and Cx. infula bred at high pH (8.19 ± 0.04 & 8.49 ± 0.13) when compared to other Culex mosquitoes. Cx. fuscocephala bred at high total dissolved solids (570.5 ± 2.5) and free carbon dioxide levels (170.5 ± 16.5). Cx. infula was observed at high conductivity (6.87 ± 1.45) and high dissolved oxygen levels (9.57 ± 0.99) when compared to other Culex mosquitoes. Among Culex mosquitoes, Cx. vishnui (34.07 ± 2.41) bred under high turbid water followed by Cx. quinquefasciatus (29.55 ± 2.99) and Cx. gelidus (26.26 ± 3.28). Cx. gelidus was found to breed only in sewage water whereas Cx. bitaeniorhynchus bred only in low turbid fresh water bodies (Table 7).

Table 6 Physico-chemical characteristics of water in breeding habitats of Anopheline and Culicine species
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Table 7 Physico-chemical characteristics of water in breeding habitats of immature Culicine species
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Grouping immature mosquito population by habitat similarity

The different species of mosquitoes were arranged into two major groups using the values of coefficient of association presented in the similarity matrix (Table 8). According to cluster analysis (Fig. 4), An. subpictus, Cx. vishnui, An. vagus, Cx. tritaeniorhynchus, Cx. gelidus, and Cx. quinquefasciatus fell under group A. The group B was divided into two sub groups namely group B1 and B2. Sub-group B1 consists of An. annularis, An. stephensi, An. splendidus, An. pallidus, Cx. fuscocephala and Aedeomyia catasticta whereas An. peditaeniatus, An. culicifacies, An. barbirostris, Cx. infula, Cx. pseudovishnui, Cx. bitaeniorhynchus, Lutzia fuscana, Stegomyia aegypti and Fr. vittatus was found under group B2. Based on habitat similarity analysis, An. subpictus and Cx. vishnui were found to have the highest association (0.961). The similarity values within the species for Group A are as follows: An. vagus/Cx. tritaeniorhynchus (0.899), Cx. vishnui/Cx. tritaeniorhynchus (0.856), Cx. tritaeniorhynchus/Cx. quinquefasciatus (0.848) and Cx. quinquefasciatus/Cx. gelidus (0.830). In Group A, An. subpictus had strongest habitat similarity with Cx. vishnui (0.961), Cx. tritaeniorhynchus (0.833), Cx. quinquefasciatus (0.818), An. vagus (0.816), and Cx. gelidus (0.731). In group B, mosquito species pairs showing high similarity were An. culicifacies with Cx. bitaeniorhynchus (0.832), An. peditaeniatus with Cx. infula (0.782), An. peditaeniatus between Cx. pseudovishnui (0.773), An. barbirostris with Lt. fuscana (0.760), Cx. infula with Cx. pseudovishnui (0.742) (Table 8). In group A, An. subpictus and Cx. vishnui were found almost in all the types of immature habitats at all the sites during the study period. It is inferred that these two species had a wide range of adaptability to habitats dominated by E. crassipes, C. rotundus, S. spontaneum, I. aquatica, P. glabrum, filamentous algae, floating algae, C. dactylon, Marsilea sp., algal bloom, Arundo donax, Lemna sp. and Azolla sp. An. subpictus, An. vagus, Cx. vishnui, Cx. tritaeniorhynchus, Cx. gelidus and Cx. quinquefasciatus were able to breed in polluted water bodies typically associated with high turbidity. As a result, the immature mosquitoes of group A have been sharing their habitats with more number of distant or closely related mosquito species along the Vaigai river (Table 9). In group B1, mosquitoes preferred unique ecological habitats along the river. An. annularis, An. stephensi, An. splendidus, An. pallidus and Ad. catasticta bred in filamentous algae dominated sites. These mosquitoes bred at low level of turbid water when compared to group A. Immature mosquitoes of group B1 utilize limited ecological niches which led us to conclude that B1 mostly don’t share their habitat with other species. In group B2, few more ecological habitats were occupied by mosquitoes when comparing to group B1. An. peditaeniatus was found to breed under various vegetation types such as floating algae, filamentous algae, E. crassipes, C. rotundus, S. spontaneum and Typha sp. Cx. pseudovishnui utilized aquatic vegetation such as E. crassipes, C. rotundus, I. aquatica, P. glabrum, filamentous algae and C. dactylon as their breeding habitats. The immature of An. barbirostris was collected from floating algae, filamentous algae, Cynodon dactylon, algal bloom, C. rotundus, S. spontaneum, Lemna sp. and Azolla sp. dominated sites. An. culicifacies bred in floating algae, filamentous algae, C. rotundus, S. spontaneum, detritus, Typha sp. and even in open water. Lt. fuscana immature was recorded in C. dactylon, C. rotundus and floating algae dominated sites. Cx. infula and Cx. bitaeniorhynchus preferentially bred in filamentous algae dominated habitats. Immature of the Group B2 was found to breed in slightly turbid water than group B1.

Table 8 Similarity matrix for the operative taxonomic units of different mosquito calculated using coefficient of association
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Fig. 4
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Grouping of immature mosquitoes based on the habitat similarity using dendrogram

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Table 9 Co-occurrence of immature mosquito species in a breeding habitat along the Vaigai river, Tamil Nadu
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Discussion

The Vaigai river is highly altered by various human activities which have consequently led to support immature mosquito populations by providing strong ecological links for their sustenance within the ecosystem (Kamaladhasan et al., 2016). Among various human activities, sewage disposal into river was found to influence water quality thereby affecting the structure and function of the ecosystems. Water pollution in river ecosystem causes loss of biodiversity by altering species composition from natural to pollutant tolerant community (Xu et al., 2013). In the present study, water quality parameters considered in this study have been found to influence the distribution and composition of mosquito populations along the Vaigai river ecosystem. Among the water quality parameters, pH plays a significant role in the habitat preference of Anopheline species. Almost all Anopheles species have been observed to breed in habitats with pH ranges between 6.95 and 10.08. Similarly, Akeju et al. (2022) reported that the pH of the breeding habitats of Anopheles species ranges between 6.05 and 8.23. This clearly reveals that Anopheline species mainly prefer to select their oviposition sites with a slightly acidic and slightly alkaline pH environment (Akeju et al., 2022; Getachew et al., 2020). Total dissolved solid has been found to be higher in urban sites than semi-urban and rural sites which are resulted alter the composition and dominance of mosquito species. In the present study, the diversity and dominance of Culex mosquitoes were highest in urban sites when compared to Anopheles species. These results clearly showed that Culex mosquitoes are able to breed with high total dissolved solids content, whereas Anopheles mosquitoes mainly opt to breed with less total dissolved solids content. These results are concurred with the findings of Vanlalhruaia et al. (2014) reported that, Anopheles species prefer habitats with less total dissolved solid compared to Culex mosquitoes, which have strong associations with high dissolved matter and total dissolved solid. However, in the present study, An. subpictus can breed in a habitat with a high level of total dissolved solids range between 0.53 and 1010, compared to other Anopheles species. This finding was in agreement with the report of Abai et al. (2015), where Anopheles mosquitoes have a strong association with high levels of total dissolved solid (1261.40 1214.31). Among the water quality parameters, salinity and conductivity can be considered as predictive variables for the existence of mosquito species. The increase in salinity and conductivity has resulted in a reduction in species diversity and an increase in the density of salinity-tolerant species (Gopalakrishnan et al., 2013; Nikookar et al., 2017). This was in agreement with the report of the present study, the diversity of Anopheles species was observed to be higher in breeding habits with less level of salinity and conductivity when compared to Culex species. However, among the Anopheles species, the density of An. subpictus gradually increased with the increase in salinity and conductivity. This is clearly showed that the An. subpictus have adapted to tolerate the high salinity environment condition. Among the Culex species, Culex gelidus can able to thrive under in high salinity habitats. Similar results were also observed in the Cx. tarsalis and Cx. quinquefasciatus (Kengne et al., 2019; Patrick & Bradley, 2000). Turbidity also plays a crucial role in the identification of breeding habitats for Anopheline and Culicine. The breeding of Anopheline species was observed in habitats with lower turbidity levels, while that of Culex species was observed in habitats with high turbidity levels. This result is concurred with the finding of Sattler et al. (2005) reported that Anopheles mosquito larvae were absent in habitats with turbid environments, whereas Culex species were much more likely to breed in such habitats. However, An. subpictus is able to breed and has a greater density in habitats with high levels of turbidity than other Anopheles species in the present study. This result is not in agreement with the finding of Seal and Chatterjee (2023), reported that, An. subpictus larvae were found to be higher in less turbid habitats when compared to highly turbid environments.

Water quality also plays a significant role on the community assemblage of immature mosquitoes along the Vaigai river basin. Community assemblage by Anopheles have found to be higher in rural sites and semi-urban sites when compared to urban sites. In rural and semi-urban sites, water bodies are less polluted which are eventually to breed by Anopheles species than polluted water bodies. This result is supported by earlier studies reported that Culicine immatures were found in polluted water and Anopheline immatures were found in less polluted water (Okorie, 1978; Okogun, 2005; Sattler et al., 2005; Devi & Jauhari, 2007; Impoinvil et al., 2008; Mwangangi et al., 2010). Community assemblage by Anopheles along with Culex species were found to be higher in all the study sites during all the season. In the present study, habitat similarity index was found to be higher between An. subpictus and Cx. vishnui (0.96) and shared their habitats with a greater number of distant or closely related species which are resulted to increased community assemblage by Anopheles along with Culex species along the Vaigai river basin. This result is coincided with the finding of Devi and Jauhari (2007) reported that Cx. mimeticus and An. maculatus have strong association with their habitats. This result was similar to the findings of Minakawa et al. (1999), Caillouet et al. (2008) who also reported that, 58.6% and 42.9% of the habitats were co-existed by Anopheline and Culicine species respectively. Grouping of immature mosquitoes based on their habitat similarity is clearly revealed that Mosquitoes belonging to group A were much more like to breed polluted water bodies when compared to Group B mosquito species. Among the group A mosquito species, An. subpictus and An. vagus have adapted to breed in polluted water bodies in addition to fresh water habitats. Similarly, some of the Anopheline species has been observed to breed in polluted water habitats across the world. For instances, An. subpictus was noted to breed in polluted habitats at urban ecosystem (Gunathilaka et al., 2015). Drainage habitats with waste water is an ideal breeding habitats for An. culicifacies (Gunathilaka et al., 2013). An. gambiae and An. coluzzii can able to breed wide range of water bodies including polluted water (Awolola et al., 2007; Ossè et al., 2019). In the present study, An. subpictus, Cx. vishnui, An. vagus, Cx. tritaeniorhynchus, Cx. gelidus, and Cx. quinquefasciatus were more prevalent species and might be significant role on the mosquito born disease outbreak along the Vaigai river basin.

Conclusions

The results of this study clearly revealed that physiochemical parameters determine the species composition and community assemblage of immature mosquitoes along the Vaigai river basin. The habitat preference of Anopheline species is greatly influenced by physiochemical parameters like pH, total dissolved solid, salinity, conductivity, and turbidity. Among the immature mosquito species, An. subpictus, and Cx. vishnui were the most prevalent species and had strong habitat similarity, which led to an increase in the community assemblage of Anopheline and Culicine species along the river ecosystem. In the present study showed for the first time An. subpictus and An. vagus can adapt to breed in polluted habitats and this may be adequate to extend the vectorial capacity and disease outbreak along the Vaigai river basin.